1. Field of the Invention
The present invention relates to a handoff system and method, between different kinds of devices, capable of achieving a seamless handoff between two devices without changing an existing session, and a Session Initiation Protocol (SIP) server and an operational method of the SIP server applied thereto.
2. Description of the Related Art
In recent years, widespread use of the Internet, rapid advances in wireless communication technology, and performance enhancement of mobile communication terminals such as portable computers and Personal Digital Assistants (PDA's) have increased the number of wireless Internet users. In a wireless Internet environment, a mobile communication terminal can be moved at any time and its network access point changed.
In order make wireless Internet communication of a mobile communication terminal possible, equally high quality Internet service should be guaranteed even though the mobile communication terminal moves from a current network area to another network area.
That is, the mobile communication terminal should be provided with seamless communication. To this end, a process called ‘handoff’ has been introduced. In telecommunications, the term handoff refers to the process of transferring an ongoing call from an access node in a current network area to an access node of another network area.
Based on this handoff function, a handoff between various devices has been proposed to provide a mobile user with the same service regardless of the type of Internet connection, even though the user changes the user's device to a different type of device as the user moves to another location.
For instance, suppose a user would now like to receive the Internet service the user had been previously receiving through a PDA, through a PC. According to a related art regarding handoff between different kinds of devices, the user must input information necessary for a handoff in order to hand off the Internet service from the PDA to the PC, and then request a handoff.
The handoff request made by the user is sent to a SIP server from the PC, and the SIP server requests a handoff of a crossover node. The crossover node then adds a session connection, whereas the PDA separates the session connection, thereby performing a handoff from the PDA to the PC.
In this case, since the user must input the information, such as a user ID, a session ID, a service speed etc., for the handoff, the user cannot request a handoff unless the user knows know the session ID of the other party. Moreover, the user is allowed to request a handoff only when the user can access both devices with the handoff function.
Also, since the crossover node is directly involved in the handoff, it is absolutely necessary for the crossover node to have a session changing function for adding a session connection to the PC and separating a session connection of the PDA.